Current emulsion polymerization processes have cyclic siloxane levels greater than one percent in the final emulsion. With a lower cyclic siloxane level, final product formulations can be better controlled.
Cyclic siloxane contaminants are undesirable from the perspective of health and safety, and there are regulations on the allowed levels in products. Additionally, cyclic siloxanes have a tendency to lower the viscosity of shampoos.
Emulsion polymerization processes have been previously reported, but prior art processes utilized either cyclic siloxanes or mixtures of cyclic and linear siloxanes, and these processes cannot produce emulsions with low cyclic siloxane levels. See, for example, U.S. Pat. No. 5,504,149, which utilizes cyclic siloxanes, surfactant and an initiator that is a silanolate or an organosilanolate; U.S. Pat. No. 4,066,594, which uses cyclic siloxanes and benzene sulfonic acid and optionally a platinum catalyst; EPA 874017, which uses a metal containing catalyst for a chain extension reaction; and JP 9278626, which uses a catalyst and heat for the emulsion polymerization. When cyclic siloxanes are used, the emulsion must be heated to allow polymerization and then cooled for condensation, and the final polymer viscosity is a function of the condensation temperature.
A process is needed in which the particle size of the emulsion can be controlled, as well as the viscosity and the level of cyclic siloxanes in the emulsion. It has been discovered that by using a neutral surfactant system instead of an acid catalyst surfactant during homogenization, particle size, viscosity and cyclic siloxanes can be controlled. A benefit is that with the lower cyclic siloxane level, a safer product can be produced.